Some say that her letter is a response to Maria Sharapova's perspective of Serena in her new memoir, 'Unstoppable: My Life So Far'

Tennis champion Serena Williams penned a heartfelt letter to her mum on Reddit yesterday. She opened up about being a first time mother while also thanking her own mum from whom she learned confidence and determination.

Dear Mum,

You are one of the strongest women I know. I was looking at my daughter (OMG, yes I have a daughter) and she has my arms and legs! My exact same strong, muscular, powerful, sensational arms and body. I don't know how I would react if she has to go through what I've gone through since I was a 15-year-old and even to this day.

I've been called man because I appeared outwardly strong. It has been said that that I use drugs (No, I have always had far too much integrity to behave dishonestly in order to gain an advantage). It has been said I don't belong in Women's sports – that I belong in Men's – because I look stronger than many other women do. (No, I just work hard and I was born with this badass body and proud of it).

But mum, I'm not sure how you did not go off on every single reporter, person, announcer and quite frankly, hater, who was too ignorant to understand the power of a black woman. I am proud we were able to show them what some women look like. We don't all look the same. We are curvy, strong, muscular, tall, small, just to name a few, and all the same: we are women and proud!

You are so classy, I only wish I could take your lead. I am trying, though, and God is not done with me yet. I have a LONG way to go, but thank you. Thank you for being the role model I needed to endure all the hardships that I now regard as challenges – ones that I enjoy. I hope to teach my baby Alexis Olympia the same, and have the same fortitude you have had.

Promise me, Mum that you will continue to help. I'm not sure if I am as meek and strong as you are yet. I hope to get there one day. I love you dearly.

While most of us would think it's a harmless letter in tribute to her mother, others speculate that it could be a sly response to Maria Sharapova's newly published memoir, Unstoppable: My Life So Far where Maria referenced Serena over 100 times.

The part of the letter where Serena mentions her "same strong, muscular, powerful, sensational arms and body" mirrors Maria's quote that says "First of all, her physical presence is much stronger and bigger than you realise watching TV... She has thick arms and thick legs and is so intimidating and strong. And tall, really tall."

Maria beat Serena twice – once at the 2004 Wimbledon tournament and at the 2004 WTA Championships. However, she has since lost to Serena 10 times in a row.